Our goal is to try to understand the roles of functionally-uncharacterized genes in M. tuberculosis. We will focus on genes that are important for the growth and survival of the bacterium under conditions likely to be relevant to infection, and use multiple approaches to define phenotypes and key interactions to reveal function. We will select targets using existing genome wide screening information. Each target will be investigated using parallel independent approaches to increase the chances of success. Our overall goal is to define function using the GO (gene ontology) definitions of molecular function, cellular process and/or biological process. We will attempt to determine as many of these as possible for each target. This will be accomplished through the following objectives: Objective 1. Identify phenotypes for underexpressing strains (with Core E) Objective 2. Identify interacting genes and proteins (with Cores, C, D and E) Objective 3. Identify substrates/products of potential enzymes (with Cores B and E) Objective 4. Confirm putative interacting genes and pathways (with Cores B-E).